Various types of chemical solutions are used extensively in the fabrication of devices and articles. Typical examples are plating solutions, solutions used to etch surfaces or holes, solutions used to prepare surfaces for various processing, etc. The success of these processes often depends critically on the exact composition of these solutions as well as other process parameters such as temperature, contact time, etc. Highly desirable is a continuous procedure for monitoring solution composition so as to insure close control of the process.
Indeed, in many modern technological processes, rapid, continuous response to composition changes is a necessity to avoid extensive loss of product and to prevent the production of defective product.
A particular example may be used in illustrating the importance of close control of solution composition in some processes. Solutions of dimethylformamide in water are used to treat polymer surfaces prior to metallization in the fabrication of substrates for circuit boards. Close control of solution composition is of critical importance. Too high a concentration of dimethylformamide in water leads to a brittle surface; too low a concentration produces insufficient swelling and often weak bonding of metal to polymer surface. Close control of solution concentration as well as temperature and exposure time yields smooth, well-bonded metallic layers suitable for use in circuit boards.
Particularly useful is a method of continuously monitoring solution composition so as to insure correct composition of solution at all times. Also useful is a feedback system to continuously and automatically adjust solution composition to a predetermined value. Various multicomponent solutions are of interest including 2-component solutions, 3-component solutions and larger-component solutions.